“HLVd is a major threat to the cannabis industry. HLVd is a highly transmissible pathogen that can be easily transmitted via mechanical means. Early and accurate diagnosis is an essential step in disease management. However, HLVd infection usually remains latent, which makes it challenging for growers to diagnose the disease at earlier stages of infection. Viroids are made of RNA only, which limits the use of detection techniques exclusively to nucleic-acid-based methods only.” Therefore, researchers from Texas A&M University established a study to expand knowledge on HLVd detection, diagnosis, host range, and transmission. “With this knowledge, we can increase the efficiency of HLVd management protocols.”
Detection
Nowadays, RT-PCR has become a commercially available technology for HLVd detection via many third-party laboratories in the United States. In this study, HLVd-specific primers were used for RT-PCR detection in plant samples and were able to detect HLVd in as little as 5 picograms of total RNA. “Our results demonstrate the high accuracy and reliability of RT-PCR assay in HLVd detection in infected hemp samples.”
Co-existence?
The researchers explain that HLVd is among several viral and subviral agents that attack hemp and cause several types of losses in product quality and total yield, such as HSVd, hemp streak virus, hemp mosaic virus, cannabis cryptic virus, and beet curly top virus. Disease symptoms can be significantly affected by pathogen populations within the same niche, and synergism or superinfection exclusions are among the widely known types of interactions among viral pathogens within plants. “We studied the possibility of co-existence between HLVd and HSVd, two of the most widely spread viroids. A survey of hemp samples obtained from a diseased production system proved sole infection of HLVd (72%) with no co-existence of hop stunt viroid.”
Infectivity
The inoculum of HLVd is infectious in several forms. “It has been previously demonstrated that either crude sap, total RNA extract, or cDNA transcripts of HLVd are infectious and can successfully aid viroid replication within hemp. We compared the infectivity of crude contagious sap versus total RNA extracts from infected hemp. HLVd sequences were detected in the roots and upper non-inoculated leaves of inoculated plants, which indicates successful movement of the viroid within the inoculated plants. Our findings added that crude sap is more effective than total RNA extract.”
Seed transmission
The study also found that HLVd was highly transmissible through hemp seeds at rates of 58 to 80%. “Seed transmission is one of the most vital means of transmission evolved by plant viruses and subviral agents to overwinter during the absence of growing plant hosts. This can be a significant cause for accidental introduction into farm production systems that are a long distance from the original source.”
To read the complete study, go to mdpi.com